Ultra-low current and/or voltage references are required in most low power circuit applications. Examples of such applications include circuits which are powered by a battery and are always on.
The area of an integrated circuit which is occupied by an ultra-low current and/or voltage generator is typically dominated by the presence of a large resistor, not the presence of the included transistors. In this regard, those skilled in the art understand that to reduce the current consumption of the generator by one-half, the size of the included resistor needs to be increased by two times. Thus, there is a known trade-off between power/current and occupied area.
A figure of merit (FOM) is known which can be used to compare current/voltage generators: FOM=TCC*A*M; where TCC is the total current consumption, A is the area of the generator circuit, and M is the Monte-Carlo mismatch of the generator circuit. It is desired to minimize the FOM. In this regard, the circuit designer desires for a same mismatch and area to reduce the current consumption, or for a same mismatch and current consumption to reduce the area. One known solution for reducing the area creates the large resistor by using a switched capacitor resistor circuit with an external clock reference. Another solution for creating a large resistor is use a MOSFET device operating in the triode region. Reference is made to U.S. Patent Application Publication No. 2007/0241809 (the disclosure of which is incorporated by reference). The foregoing solutions are not, however, satisfactory.